Diffusive Transport Processes Research Articles

Multivalent Diffusive Transport

We present here a model for multivalent diffusive transport whereby a central point-like hub is coupled to multiple feet, which bind to complementary sites on a two-dimensional landscape. The available number of binding interactions is dependent on the number of feet (multivalency) and on their allowed distance from the central hub (span). Using Monte Carlo simulations that implement the Gillespie algorithm, we simulate multivalent diffusive transport processes for 100 distinct walker designs. Informed by our simulation results, we derive an analytical expression for the diffusion coefficient of a general multivalent diffusive process as a function of multivalency, span, and dissociation constant Kd. Our findings can be used to guide the experimental design of multivalent transporters, in particular, providing insight into how to overcome trade-offs between diffusivity and processivity.

Quantitative 3D Characterization of Nanoporous Gold Nanoparticles by Transmission Electron Microscopy.

Quantitative structural characterization of nanomaterials is important to tailor their functional properties. Corrosion of AgAu-alloy nanoparticles (NPs) results in porous structures, making them interesting for applications especially in the fields of catalysis and surface-enhanced Raman spectroscopy. For the present report, structures of dealloyed NPs were reconstructed three-dimensionally using scanning transmission electron microscopy tomography. These reconstructions were evaluated quantitatively, revealing structural information such as pore size, porosity, specific surface area, and tortuosity. Results show significant differences compared to the structure of dealloyed bulk samples and can be used as input for simulations of diffusion or mass transport processes, for example, in catalytic applications.

Expanded Hemodialysis: Promising Prospects

End stage kidney disease (ESKD) causes accumulation of uremic toxins which cover a wide range of molecules classified according to molecular weight into small molecules (<500 Da), medium-sized molecules (500 Da – 60 kDa) and protein-bound toxins.Hemodialysis (HD) remains the main modality of renal replacement therapy in ESKD. Preferably used low-flow dialyzers provided removal of small soluble substances by diffusion, but not clearance of medium-sized molecules.The situation has changed somewhat with the advent of high-flow membranes (HF) and, later, online hemodiafiltration (ol-HDF) which significantly increased the clearance of small and medium-sized molecules due to a combination of diffusion and convection.There is some evidence confirming the hypothesis of insufficient clearance of uremic toxins with higher molecular weight by conventional HD which is the cause of high rates of comorbidity and mortality in patients with ESKD.Specific complications of HD are associated with the accumulation of medium-sized molecules, including myoglobin, leptin, prolactin, fibroblast growth factor (FGF) 23, free light chains kappa and lambda (FLC). Moreover, molecules bound to the proteins like homocysteine, oxidative stress mediators and inflammatory cytokines accelerate the development of atherosclerosis and, as a result, increase cardiovascular mortality.The introduction of MCO membranes into clinical practice has made it possible to develop a new concept of HD therapy called “expanded hemodialysis” (HDx).Thus, new technological solutions concerning the composition of the MCO dialysis membrane enabled to change the dialysis therapeutic targets and combine the capabilities of diffusion and convective transport processes to affect them. Preliminary results demonstrate positive effect of HDx on the triggers of a range of mechanisms of dialysis-associated comorbidity and mortality which can potentially significantly reduce their frequency and/or rate of progression.

Tracing the ionic evolution during ILG induced phase transformation in strontium cobaltite thin films

Ionic liquid gating (ILG) that drives the ions incorporate into or extract from the crystal lattice, has emerged as a new pathway to design materials. Although many intriguing emergent phenomena, novel physical properties and functionalities have been obtained, the gating mechanism governing the ion and charge transport remains unexplored. Here, by using the model system of brownmillerite SrCoO2.5 and the corresponding electric-field controlled tri-state phase transformation among the pristine SrCoO2.5, hydrogenated HSrCoO2.5 and oxidized perovskite SrCoO3−δ through the dual ion switch, the ionic diffusion and electronic transport processes were carefully investigated. Through controlling gating experiment by design, we find out that the collaborative interaction between charge transport and ion diffusion plays an essential role to prompt the hydrogen or oxygen ions incorporate into the crystal lattice of SrCoO2.5, and therefore leading to formation of new phases. At region closer to the electrode, the electron can shuttle more readily in (out) the material, correspondingly the incorporation of hydrogen (oxygen) ions and phase transformation is largely affiliated. With the compensated charge of electron as well as the reaction front gradually moving away from the electrode, the new phases would be developed successively across the entire thin film. This result unveils the underlying mechanism in the electric-field control of ionic incorporation and extraction, and therefore provides important strategy to achieve high efficient design of material functionalities in complex oxide materials.

A Pore Network Model of Carbon-Based Electrodes for Redox Flow Batteries

Electrodes constitute one of the main components of Redox Flow Batteries (RFBs) since they represent the sites where the electrochemical reaction occurs. The development of optimized electrode microstructures is therefore crucial in the design of the next generation RFBs.[1] For this purpose, there has been a surge in interest to understand the effect of the reactive and mass transport processes occurring within electrodes. Previous authors have introduced pore-scale models which perform direct numerical simulations of the multi-physics processes over reconstructed images of electrode microstructure; however, these models require high processing power and take significant time to converge.[2] In search of computationally inexpensive models the pore-scale detail of the microstructure, pore network models (PNMs) are considered a compelling alternative. [3]In this work, a computationally efficient PNM is developed to represent the multi-physics processes occurring within porous carbon electrodes at the pore-scale. The model solves the velocity field within the porous matrix and successively couples the mass transport equations (i.e. for convection, diffusion and migration) with the electrochemical reaction (i.e. Butler-Volmer equation). [4] The PNM algorithm is validated on a cubic framework to represent the cathode of a Vanadium Redox Flow Battery (VRFB) operating under discharge conditions at 400 A m-2. These results are compared against the reported values of half-cell potentials of the same system, showing a good fit [5] (Figure 1 (a)). The PNM is subsequently implemented on pore networks extracted from X-ray computed tomography (X-CT) images of two commercial porous carbon electrodes: Toray090 (Figure 1 (b)) and SGL29AA. In both cases, the results show non-uniformity in the concentration and pressure distributions across the electrode when considering the pure convective and diffusive transport processes. The existence of preferred electrolyte travel pathways through the interconnected pores and throats is simulated and visually shown. The migration and reactive processes are subsequently considered and are shown to be influenced by the rate at which the convective/diffusive flow permeates the electrode. These results demonstrate how the rate at which electrolyte is replenished is affected by the interconnectivity between pores: in both carbon electrodes, the regions with low interconnectivity induce slow replenishment, which leads to reactant. This process represents a pore-scale transport limitation that results in the localized reduction of current density upon discharge. Furthermore, the simulation was run for these two electrodes at two pressure drops () and show that, even at relatively high convective flow, the electrolyte follows preferred paths, leading to a non-uniform utilization of the electrode and the existence of “convection-limited ” where almost no electrolyte permeates, (Figure 1(c))To conclude, this PNM algorithm pore-scale transport processes within the electrode showing the effect of interpore connectivity on electrode utilization. The results suggest that an electrode with higher interpore connectivity would allow an even distribution of electrolyte, reducing transport limitations and reactant starvation. The simulations were performed on a standard single core workstation, and converged in 15 minutes, highlighting the benefits of using a computationally inexpensive pore-scale model. Chakrabarti, D. Nir, V. Yufit, F. Tariq, J. Rubio-Garcia, R. Maher, A. Kucernak, P. V. Aravind and N. P. Brandon, ChemElectroChem, 4, 194 (2017).Qiu, A.S. Joshi, C.R. Dennison, K.W. Knehr, E.C. Kumbur and Y. Sun, Electrochimica Acta, 64, 46 (2012).T. Gostick, M. A. Ioannidis, M. W. Fowler and M. D. Pritzker, Journal of Power Sources, 173(1), 277 (2007).Gayon Lombardo, B.A. Simon, O.O. Taiwo, S.J. Neethling and N.P. Brandon, Journal of Energy Storage, 24, 100736 (2019).You, H. Zhang, and J. Chen, Electrochimica Acta, 54(27), 6827 (2009). Figure 1

Elucidation of Densification Experienced By LLZO Solid Electrolytes

In order to improve the energy density and minimize the safety concerns associated with the liquid electrolytes used in the present day lithium ion batteries, solid electrolytes are being actively considered for use in the next generation energy storage devices.[1] Among various ceramic based solid state electrolytes being investigated, Li7La3Zr2O12 (LLZO) with a garnet crystal structure demonstrates very high ionic conductivity and is extremely stable against lithium.[2] Hence, LLZO is being actively considered as the electrolyte for next generation lithium ion batteries. However, due to poor processing of these ceramics, they contain pores and voids.[3] These open spaces within the bulk not only decrease the effective conductivity of the electrolyte, but also provides open pathways for Li dendrites to propagate. Presence of pores within the ceramic structure can be estimated from the final relative density of the solid electrolyte. High temperature sintering induced densification of the LLZO particles are conducted to improve the relative density of the final solid electrolyte, and this process helps to minimize the void space within the structure.[3, 4] Sometime external pressures are applied to further improve the relative densities.[5] Even though several experimental studies have been conducted for constructing the LLZO solid electrolytes, very little effort has been devoted to actually understand the physical mechanisms that play major role during the densification process.In the present context, a computational methodology has been developed at the mesoscale level to understand the impact of surface and grain-boundary diffusion mechanisms on the overall grain ripening and densification experienced by the LLZO solid electrolytes during the sintering process conducted at elevated temperatures. During densification, the extent of increase in relative density depends on the activation energy associated with the diffusive mass transport processes. Here, the activation energy for LLZO will be estimated from direct comparison of relative densities obtained from the developed computational model and experimental observations.[6] Some strategies, in terms of particle sizes and size distributions, that can lead to improved relative densities within the LLZO solid electrolytes, will also be discussed in this presentation. References Zhang, Z., et al., New horizons for inorganic solid state ion conductors. Energy & Environmental Science, 2018. 11(8): p. 1945-1976. Ramakumar, S., et al., Lithium garnets: synthesis, structure, Li+ conductivity, Li+ dynamics and applications.Progress in Materials Science, 2017. 88: p. 325-411. Rangasamy, E., J. Wolfenstine, and J. Sakamoto, The role of Al and Li concentration on the formation of cubic garnet solid electrolyte of nominal composition Li7La3Zr2O12. Solid State Ionics, 2012. 206: p. 28-32. Sharafi, A., et al., Controlling and correlating the effect of grain size with the mechanical and electrochemical properties of Li7La3Zr2O12 solid-state electrolyte. Journal of Materials Chemistry A, 2017. 5(40): p. 21491-21504. Dzepina, B., D. Balint, and D. Dini, A phase field model of pressure-assisted sintering. Journal of the European Ceramic Society, 2019. 39(2-3): p. 173-182. Shin, R.-H., et al., Effect of Li3BO3 additive on densification and ion conductivity of garnet-type Li7La3Zr2O12 solid electrolytes of all-solid-state lithium-ion batteries. Journal of the Korean Ceramic Society, 2016. 53(6). Figure 1

Simulation of diffusive uranium transport and sorption processes in the Opalinus Clay

Diffusive transport and sorption processes of uranium in the Swiss Opalinus Clay were investigated as a function of partial pressure of carbon dioxide pCO2, varying mineralogy in the facies and associated changes in porewater composition. Simulations were conducted in one-dimensional diffusion models on the 100 m-scale for a time of one million years using a bottom-up approach based on mechanistic surface complexation models as well as cation exchange to quantify sorption. Speciation calculations have shown, uranium is mainly present as U(VI) and must therefore be considered as mobile for in-situ conditions. Uranium migrated up to 26 m in both, the sandy and the carbonate-rich facies, whereas in the shaly facies 16 m was the maximum. The main species was the anionic complex CaUO2(CO3)32−. Hence, anion exclusion was taken into account and further reduced the migration distances by 30 %. The concentrations of calcium and carbonates reflected by the set pCO2 determine speciation and activity of uranium and consequently the sorption behaviour. Our simulation results allow for the first time to prioritize on the far-field scale the governing parameters for diffusion and sorption of uranium and hence outline the sensitivity of the system. Sorption processes are controlled in descending priority by the carbonate and calcium concentrations, pH, pe and the clay mineral content. Therefore, the variation in porewater composition resulting from the heterogeneity of the facies in the Opalinus Clay formation needs to be considered in the assessment of uranium migration in the far field of a potential repository.

Assessing multi-regime combustion in a novel burner configuration with large eddy simulations using tabulated chemistry

Recent investigations on a novel multi-regime burner (MRB) configuration showed significant deviations in the CO flame structure compared to the limiting cases of premixed and non-premixed flames. However, a prior analysis revealed that major species and temperature are captured by both limiting cases (Butz et al., Combust. Flame, 2019 [1]). In the present work, large eddy simulations using an artificial thickened flame approach and tabulated chemistry are performed for the MRB configuration. Simulation results are compared to experimental Raman/Rayleigh/CO-LIF and PIV measurements, confirming the applicability of the modeling approach. Further, simulation results are consistent with the aforementioned prior analysis. Special attention is paid to predicting CO by analyzing the conditional flame structure and the effects of local residence time. This combined CO and residence time analysis reveals that local convective and diffusive transport processes should be resolved simultaneously with the unsteady flow, instead of being tabulated. Substantial improvements in CO are achieved when local transport is considered.

Finite Difference Approximation Method for a Space Fractional Convection–Diffusion Equation with Variable Coefficients

Space non-integer order convection–diffusion descriptions are generalized form of integer order convection–diffusion problems expressing super diffusive and convective transport processes. In this article, we propose finite difference approximation for space fractional convection–diffusion model having space variable coefficients on the given bounded domain over time and space. It is shown that the Crank–Nicolson difference scheme based on the right shifted Grünwald–Letnikov difference formula is unconditionally stable and it is also of second order consistency both in temporal and spatial terms with extrapolation to the limit approach. Numerical experiments are tested to verify the efficiency of our theoretical analysis and confirm order of convergence.

Convective Phenomena in Mushy Layers

Since the Annual Review of Fluid Mechanics review of mushy layers by Worster (1997) , there have been significant advances in the understanding of convective processes in mushy layers. These advances have come in the areas of ( a) more detailed analysis, computation, and understanding of convective instabilities and chimney convection in binary alloys; ( b) investigations of diffusive and convective transport processes in ternary alloys; and ( c) applications of mushy layer theory in materials science, sea ice, and polar climate modeling, as well as other geophysical applications such as the convective dynamics of the Earth's core. Our objective for this review is to provide an updated account of the understanding of mushy layer convection and related applications and, in doing so, to provide a new resource to the fluid dynamics research community interested in these complex systems.

High order numerical schemes for solving fractional powers of elliptic operators

In many recent applications when new materials and technologies are developed it is important to describe and simulate new nonlinear and nonlocal diffusion transport processes. A general class of such models deals with nonlocal fractional power elliptic operators. In order to solve these problems numerically it is proposed (Vabishchevich, 2015) to consider equivalent local nonstationary initial value pseudo-parabolic problems. Previously such problems were solved by using the standard implicit backward and symmetrical Euler methods. In this paper we use the one-parameter family of three-level finite difference schemes for solving the initial value problem for the first order nonstationary pseudo-parabolic problem. The fourth-order approximation scheme is developed by selecting the optimal value of the weight parameter. The results of the theoretical analysis are supplemented by results of extensive computational experiments.

Multiple steady state co-rotating dust vortices in streaming plasma

The 2D vorticity–stream function hydrodynamic model is applied to dust clouds electrostatically confined in an unbounded and streaming plasma. The vortex flow structure of the volumetrically driven dust cloud is analyzed systematically for different aspect ratios (ARs) of the bounded dust domain, exploring linear and nonlinear regimes of flow for a range of the kinematic viscosity. These results show the interplay between inertial and diffusive transport processes involving structural changes in dust vortex flow that develops asymmetry and shows a regular sequence of structural bifurcations at threshold kinematic viscosity corresponding to a change in the AR value by nearly an integer. Agreement with many experimental observations is recovered, where the generation of newer self-similar multiple co-rotating vortices is observed. The exclusive dependence of subsequent structural transitions on the flow domain AR is analyzed based on the properties of numerical solutions. These nonlinear solutions allow understanding of the underlying nonlinear characteristics of self-similar co-rotating vortices in experiments and their behavioral similarities with various relevant complex driven–dissipative natural systems.

Towards Blue Long-Lasting Luminescence of Eu/Nd-Doped Calcium-Aluminate Nanostructured Platelets via the Molten Salt Route.

Calcia-alumina binary compounds doped with rare earths and some transition metals cations show persistent luminescence from the visible to the infrared range. Specifically, the blue light can be obtained through the Eu2+ activator center in a potential host, such as dodecacalcium hepta-aluminate (Ca12Al14O33) and monocalcium aluminate (CaAl2O4). By doping with Nd3+, the persistent luminescence can be substantially prolonged; for this reason, the Eu/Nd pair is a potential choice for developing long-lasting blue luminescence. Herein, the phase evolution of the calcia-alumina system via molten salt synthesis is reported as a function of the synthesis temperature and the atmospheric environment. The fraction of CaAl2O4 phase increases when the temperature is higher. Synthesized microparticles of platelet-type morphology represent isolated nanostructured ceramic pieces. Under visible light, the particles are white. This indicates that the followed process solves the dark-gray coloring of phosphor when is synthesized in a reduced atmosphere at high temperature. As regards the synthesis mechanism, which is assisted by the molten flux, the dissolution−diffusion transport process is promoted at the surface of the alumina microparticles. In fact, the emission intensity can be modulated through the phase of the Eu-doped calcium-aluminate discrete platelets synthesized. Consequently, the photoluminescence intensity depends also on the oxidation state of the Eu ion. X-ray absorption near-edge structure and photoluminescence measurements corroborate the Eu reduction and the grain coarsening with the enhancement of the blue emission. The doped phosphors with Eu/Nd show a broad and strong absorption in the region of 320–400 nm and a broad emission band at around 440 nm when they are excited in this absorption range. From a broader perspective, our findings prove that the Ca12Al14O33 and CaAl2O4 phases open new opportunities for research into the design of blue long-lasting emitters for a wide range of fields from ceramic to optoelectronic materials.

Turbulent particle pair diffusion: Numerical simulations.

A theory for turbulent particle pair diffusion in the inertial subrange [Malik NA, PLoS ONE 13(10):e0202940 (2018)] is investigated numerically using a Lagrangian diffusion model, Kinematic Simulations [Kraichnan RH, Phys. Fluids 13:22 (1970); Malik NA, PLoS ONE 12(12):e0189917 (2017)]. All predictions of the theory are observed in flow fields with generalised energy spectra of the type, E(k) ∼ k−p. Most importantly, two non-Richardson regimes are observed: for short inertial subrange of size 102 the simulations yield quasi-local regimes for the pair diffusion coefficient, ; and for asymptotically infinite inertial subrange the simulations yield non-local regimes , with γ intermediate between the purely local scaling γl = (1 + p)/2 and the purely non-local scaling γnl = 2. For intermittent turbulence spectra, E(k) ∼ k−1.72, the simulations yield , in agreement with the revised 1926 dataset [Richardson LF, Proc. Roy. Soc. Lond. A 100:709 (1926); Malik NA, PLoS ONE 13(10):e0202940 (2018)]. These results lend support to the physical picture proposed in the new theory that turbulent diffusion in the inertial subrange is governed by both local and non-local diffusion transport processes.

Magnetization exchange in a single pore due to diffusion in internal fields: Simulation and experiment

Nuclear magnetic resonance measurements of spin relaxation are used in studies of liquid-saturated porous media where multidimensional relaxation correlations probe interpore diffusion and other transport processes. However, the magnetic susceptibility contrast between the solid and liquid results in pore-scale field inhomogeneities that influence all measurements of transverse ${T}_{2}$ relaxation time. In a previous publication we conjectured that experimentally observed exchange phenomena can correspond to intrapore diffusion between localized volumes of coherent magnetization generated by these internal gradients, rather than interpore diffusion. Here, we use a finite-element method to explore the decay of magnetization in a single pore (interstice between spheres) for the Carr-Purcell-Meiboom-Gill and two-dimensional ${T}_{2}\text{\ensuremath{-}}{T}_{2}$ exchange experiments. These simulations permit direct visualization of the time-dependent distribution of magnetization in the pore. The chosen grain size and susceptibility contrast are matched to values for Bentheimer sandstone, allowing for a comparison of simulated and experimental results. Despite the simplicity of the model pore geometry, the salient features of the magnetization decay observed experimentally are reproduced in simulation. We demonstrate that intrapore magnetization transfer can explain observations of diffusive exchange in porous materials characterized by a monomodal pore size distribution and large internal gradients.

A pore network model of porous electrodes in electrochemical devices

• A PNM is computationally efficient for analysing flow and transport processes in electrodes. • The concentration profile of electrolyte is non-uniform across the 3D electrode. • Pore size distribution and connectivity influence the intrusion of electrolyte in the electrode. • Current density across the electrode is non-uniform and related to the concentration profiles. A computationally efficient pore network model (PNM) has been developed to incorporate the transport and electrochemical phenomena occurring within porous electrodes. This PNM is validated on a synthetic cubic structure and subsequently run on a network obtained from X-ray computed tomography (X-CT) images of a sample of commercial porous carbon paper commonly used in electrochemical devices. The carbon paper's physical characteristics (pore-size distribution, permeability, porosity and electroactive surface area) are discussed. The concentration distribution of active species is examined considering solely the transient convective and diffusive transport processes initially, and subsequently is compared to the concentration of active species when migration and reactive transport factors are included. The results show non-uniformity in the concentration and pressure distributions in the electrode when considering the pure convective/diffusive transport processes. The migration and reactive processes are subsequently considered and are shown to be influenced by the rate in which the convective/diffusive flow permeates the electrode. A uniform steady decline in volume-averaged state of charge is shown, followed by a pore-scale non-uniform current density and state of charge distribution upon discharge. These results were obtained on a standard single core workstation highlighting the benefits of using a computationally inexpensive model.

Solution NMR to Quantify Mobility in Membranes: Diffusion, Protrusion, and Drug Transport Processes.

Lipid bilayer membranes are soft, fluid, and dynamic architecture where molecules are constantly moving and thermally fluctuating under physiological conditions. In this review, a strategy to quantify molecular dynamics in membranes is introduced by utilizing solution-state NMR spectroscopy as a versatile, noninvasive technique. The dynamics involves lateral diffusion and protrusion motion, in parallel and vertical direction to the membrane surface. Dynamical behavior of small-sized drugs, chemicals, and peptides is also reviewed in relation to the lipid movements in membranes, on the basis of recent multinuclear NMR in combination with the pulsed field gradient technique. Finally, in-cell NMR method is introduced as a promising technique to capture drug transport processes in real time, to shed light on mechanisms of deliveries to living cells without perturbation of the system.

Interbasin and Intrabasin Competitions Control Drainage Network Density

AbstractThe growth and evolution of drainage networks are controlled by erosional and depositional processes forced by climate and tectonics operating on the landscape. By analyzing the data from 137 natural basins across the United States and an ensemble of synthetic terrains generated by a numerical landscape evolution model, we observed a power law relationship between the characteristic length (the length scale at which the timescales of diffusive and advective transports are equal) and drainage density (total channel length divided by drainage area) with two scaling regimes. The observed regimes exhibit significantly different characteristics in terms of intrabasin (i.e., the interaction between channels and hillslopes) and interbasin (i.e., the interaction between adjacent basins) competitions. Our findings reveal the relationship between drainage density and basic geomorphic and topologic characteristics, which encapsulate the advective and diffusive transport processes acting on the landscape.

Jovian electrons in the inner heliosphere

Context. Since the Pioneer 10 flyby of Jupiter it has become well known that electrons of Jovian origin dominate the lower MeV range of charged energetic particles in the inner heliosphere. Aims. Because the Jovian source can be treated as point-like in numerical models, many attempts to investigate charged particle transport in the inner heliosphere have utilized Jovian electrons as test particles. The reliability of the derived parameters for convective and diffusive transport processes are therefore highly dependent on an accurate estimation of the Jovian source spectrum. In this study we aim to provide such an estimation. Methods. In this study we have proposed a new electron source spectrum, specified at the boundary of the Jovian magnetosphere, fitted to flyby measurements by Pioneer 10 and Ulysses, with a spectral shape also in agreement with measurements at Earth’s orbit by Ulysses, Voyager 1, ISEE and SOHO. Results. The proposed spectrum is consistent with all previous theoretical suggestions, but deviates considerably in the lower MeV range which was inaccessible to those studies.

Evaluating the hydraulic and transport properties of peat soil using pore network modeling and X-ray micro computed tomography

Micro-scale properties of peat pore space and their influence on hydraulic and transport properties of peat soils have been given little attention so far. Characterizing the variation of these properties in a peat profile can increase our knowledge on the processes controlling contaminant transport through peatlands. As opposed to the common macro-scale (or bulk) representation of groundwater flow and transport processes, a pore network model (PNM) simulates flow and transport processes within individual pores. Here, a pore network modeling code capable of simulating advective and diffusive transport processes through a 3D unstructured pore network was developed; its predictive performance was evaluated by comparing its results to empirical values and to the results of computational fluid dynamics (CFD) simulations. This is the first time that peat pore networks have been extracted from X-ray micro-computed tomography (µCT) images of peat deposits and peat pore characteristics evaluated in a 3D approach. Water flow and solute transport were modeled in the unstructured pore networks mapped directly from µCT images. The modeling results were processed to determine the bulk properties of peat deposits. Results portray the commonly observed decrease in hydraulic conductivity with depth, which was attributed to the reduction of pore radius and increase in pore tortuosity. The increase in pore tortuosity with depth was associated with more decomposed peat soil and decreasing pore coordination number with depth, which extended the flow path of fluid particles. Results also revealed that hydraulic conductivity is isotropic locally, but becomes anisotropic after upscaling to core-scale; this suggests the anisotropy of peat hydraulic conductivity observed in core-scale and field-scale is due to the strong heterogeneity in the vertical dimension that is imposed by the layered structure of peat soils. Transport simulations revealed that for a given solute, the effective diffusion coefficient decreases with depth due to the corresponding increase of diffusional tortuosity. Longitudinal dispersivity of peat also was computed by analyzing advective-dominant transport simulations that showed peat dispersivity is similar to the empirical values reported in the same peat soil; it is not sensitive to soil depth and does not vary much along the soil profile.